Functional signal line overdrive

ABSTRACT

Devices and techniques are disclosed herein to compensate for variance in one or more electrical parameters across multiple signal lines of an array of memory cells. A compensation circuit can provide a bias signal to a first one of the multiple signal lines, the bias signal having an overdrive voltage greater than a target voltage by a selected increment for a selected overdrive period.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.16/290,398, filed 1 Mar. 2019, which claims the benefit of priority toU.S. Application Ser. No. 62/787,018, titled “Functional Signal LineOverdrive”, filed 31 Dec. 2018, each of which are incorporated herein byreference in their entireties.

BACKGROUND

Memory devices are semiconductor circuits that provide electronicstorage of data for a host system (e.g., a computer or other electronicdevice). Memory devices may be volatile or non-volatile. Volatile memoryrequires power to maintain data, and includes devices such asrandom-access memory (RAM), static random-access memory (SRAM), dynamicrandom-access memory (DRAM), or synchronous dynamic random-access memory(SDRAM), among others. Non-volatile memory can retain stored data whennot powered, and includes devices such as flash memory, read-only memory(ROM), electrically erasable programmable ROM (EEPROM), erasableprogrammable ROM (EPROM), resistance variable memory, such as phasechange random access memory (PCRAM), resistive random-access memory(RRAM), or magnetoresistive random access memory (MRAM), among others.

Host systems typically include a host processor, a first amount of mainmemory (e.g., often volatile memory, such as DRAM) to support the hostprocessor, and one or more storage systems (e.g., often non-volatilememory, such as flash memory) that provide additional storage to retaindata in addition to or separate from the main memory.

A storage system, such as a solid-state drive (SSD), a Universal FlashStorage (UFS™) device, a MultiMediaCard (MMC) solid-state storagedevice, an embedded MMC device (eMMC), etc., can include a memorycontroller and one or more memory devices, including a number of dies orlogical units (LUNs). In certain examples, each die can include a numberof memory arrays and peripheral circuitry thereon, such as die logic ora die processor. The memory controller can include interface circuitryconfigured to communicate with a host (e.g., the host processor orinterface circuitry) through a communication interface (e.g., abidirectional parallel or serial communication interface). The memorycontroller can receive commands or operations from the host system inassociation with memory operations or instructions, such as read orwrite operations to transfer data (e.g., user data and associatedintegrity data, such as error data or address data, etc.) between thememory devices and the host, erase operations to erase data from thememory devices, perform drive management operations (e.g., datamigration, garbage collection, block retirement), etc.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 illustrates an example host system including a host and a storagesystem.

FIG. 2 illustrates an example 3D NAND architecture semiconductor memoryarray including N word lines and first and second select gates stackedbetween a source line and M bit lines.

FIG. 3 illustrates an example distributed RC line having a time constantcharacterized as a product of the resistance and capacitance of thedistributed RC line.

FIG. 4 illustrates example settling times of signal lines with andwithout overdrive.

FIG. 5 illustrates an example relationship between a normalizedoverdrive period and an overdrive coefficient for stacked word lines ina memory array.

FIG. 6 illustrates an example compensation profile including trim valuesfor a number of word lines across a number of memory arrays.

FIGS. 7-9 illustrate example functional compensation profiles determinedusing different compensation techniques.

FIG. 10 illustrates an example method to compensate for variance in anelectrical parameter across a number of signal lines of a memory array.

FIG. 11 illustrates an example schematic diagram of a 3D NANDarchitecture semiconductor memory array.

FIG. 12 illustrates an example block diagram of a memory module.

FIG. 13 illustrates a block diagram of an example machine upon which anyone or more of the techniques discussed herein may perform.

DETAILED DESCRIPTION

Signal lines, such as word lines or bit lines, are typically biased to atarget condition (e.g., a target voltage), such as using one or moredriver circuits, to perform certain memory operations (e.g., readoperations, write operations, etc.). A signal line can be biased above atarget condition for a duration of time to reduce a settling time of thesignal line to the target condition (e.g., a delay in the voltage of thesignal line reaching the target condition), such as disclosed in thecommonly assigned Tabriz et al. U.S. Pat. No. 9,646,662, titled“Apparatuses, Circuits, and Methods for Biasing Signal Lines,” which ishereby incorporated by reference in its entirety, including itsdisclosure of reducing propagation delay of a bias voltage on a signalline of a mHemory array. In other examples, a signal line can beunderbiased to a target condition, such as from a first target conditionto a second, lower target condition.

The present inventors have recognized, among other things, systems,apparatus, and methods to further improve memory array and memory systemperformance using functional signal line overdrive (e.g., or underdrive)to reduce performance variance across a memory array, such as settlingtime variance across signal lines of the memory array. For example,instead of determining or storing specific overdrive values (e.g., anoverdrive coefficient, an overdrive period, etc.) for each signal lineof a memory array (or an array of memory cells) or a memory system, afunctional representation of the individual values can be determined orstored. Signal lines can include word lines, bit lines, or one or moreother signal lines of a memory device. Although described herein withrespect to word lines, such devices and techniques can be applied toother signal lines of a memory system, such as bit lines, etc.

Devices and techniques are disclosed herein to compensate for variancein one or more electrical parameters across a number of signal lines(e.g., word lines) of a memory array. In an example, a compensationcircuit can provide a bias signal to a first one of the number of signallines, the bias signal having a magnitude greater than a magnitude of atarget condition by an overdrive coefficient for an overdrive periodaccording to a functional compensation profile. In an example, thefunctional compensation profile can be determined for a memory array, amemory system, specific types of memory arrays and systems, or a groupof signal lines. The functional compensation profile can be used, incombination with one or more determined electrical parameters of amemory array, such as a resistance (R) (e.g., R_(MAX), R_(MIN), etc.), acapacitance (C) (e.g., C_(MAX), C_(MIN), etc.), or one or moreelectrical parameters, to determine the overdrive values for a specificsignal line of a specific memory array. In an example, the functionalcompensation profile can be used to fix a first overdrive parameter,such as a first one of an overdrive coefficient or an overdrive period,and create a distribution for a second overdrive parameter, such as asecond one of the overdrive coefficient or the overdrive period, inaccordance with the variance of the electrical parameters across anumber of signal lines of a memory array. In other examples, thefunctional compensation profile can include multiple overdriveparameters (e.g., an overdrive coefficient, an overdrive period, etc.).In an example, the fixed parameter can be stored as a part of thecompensation or functional compensation profile, or elsewhere outside ofthe compensation or functional compensation profile. As the values ofthe variable parameter or parameters depend on the fixed value, thefixed parameter, in certain examples, can still be considered a part ofthe compensation or functional compensation profile, even when the fixedparameter is not stored directly with the variable parameter orparameters.

Software (e.g., programs), instructions, operating systems (OS), andother data are typically stored on storage systems and accessed by mainmemory for use by a host processor. Main memory (e.g., RAM) is typicallyfaster, more expensive, and a different type of memory device (e.g.,volatile) than a majority of the memory of the storage systems (e.g.,non-volatile, such as an SSD, a UFS, an eMMC, etc.). In addition to themain memory, host systems can include different levels of volatilememory, such as a group of static memory (e.g., a cache, often SRAM),often faster than the main memory, in certain examples configured tooperate at speeds close to or exceeding the speed of the host processor,but with lower density and higher cost than the main memory. In otherexamples, more or less levels or quantities of main memory or staticmemory can be used, depending on desired host system performance, size,complexity, or cost.

FIG. 1 illustrates an example system (e.g., a host system) 100 includinga host 105 and a storage system 110 configured to communicate over acommunication interface (I/F) 115 (e.g., a bidirectional parallel orserial communication interface). The host 105 can include a hostprocessor 106 (e.g., a host central processing unit (CPU) or otherprocessor or processing device) or other host circuitry (e.g., a memorymanagement unit (MMU), interface circuitry, etc.). In certain examples,the host 105 can include a main memory 108 (e.g., DRAM, etc.) andoptionally, a static memory 109, to support operation of the hostprocessor 106.

The storage system 110 can include a solid-state drive (SSD), auniversal flash storage (UFS) device, an embedded MMC (eMMC) device, orone or more other memory devices. For example, if the storage system 110includes a UFS device, the communication interface 115 can include aserial bidirectional interface, such as defined in one or more JointElectron Device Engineering Council (JEDEC) standards (e.g., JEDECstandard D223D (JESD223D), commonly referred to as JEDEC UFS HostController Interface (UFSHCI) 3.0, etc.). In another example, if thestorage system 110 includes an eMMC device, the communication interface115 can include a number of parallel bidirectional data lines (e.g.,DAT[7:0]) and one or more command lines, such as defined in one or moreJEDEC standards (e.g., JEDEC standard D84-B51 (JESD84-A51), commonlyreferred to as JEDEC eMMC standard 5.1, etc.), in other examples, thestorage system 110 can include one or more other memory devices, or thecommunication interface 115 can include one or more other interfaces,depending on the host 105 and the storage system 110.

The storage system 110 can include a memory controller 111 and anon-volatile memory 112. In an example, the non-volatile memory 112 caninclude a number of memory devices (e.g., dies or LUNs), such as one ormore flash memory devices, etc., each including periphery circuitrythereon, and controlled by the memory controller 111. Flash memorydevices typically include one or more groups of one-transistor, floatinggate memory cells. Two common types of flash memory array architecturesinclude NAND and NOR architectures. Memory cells in the memory array aretypically arranged in a matrix. The gates of each memory cell in a rowof the array are coupled to an access line (e.g., a word line). In NORarchitecture, the drains of each memory cell in a column of the arrayare coupled to a data line (e.g., a bit line). In NAND architecture, thedrains of each memory cell in a column of the array are coupled togetherin series, source to drain, between a source line and a bit line.

In three-dimensional (3D) architecture semiconductor memory devicetechnology, vertical floating gate or charge trapping storage structurescan be stacked, increasing the number of tiers, physical pages, andaccordingly, the density of memory cells in a memory device. Each memorycell in a NOR, NAND, 3D Cross Point, HRAM, MRAM, or one or more otherarchitecture semiconductor memory array can be programmed individuallyor collectively to one or a number of programmed states. A single-levelcell (SLC) can represent one bit of data per cell in one of twoprogrammed states (e.g., 1 or 0). A multi-level cell (MLC) can representtwo or more bits of data per cell in a number of programmed states(e.g., 2^(n), where n is the number of bits of data). In certainexamples, MLC can refer to a memory cell that can store two bits of datain one of 4 programmed states. A triple-level cell (TLC) can representthree bits of data per cell in one of 8 programmed states. A quad-levelcell (QLC) can represent four bits of data per cell in one of 16programmed states. In other examples, MLC can refer to any memory cellthat can store more than one bit of data per cell, including TLC andQLC, etc.

The non-volatile memory 112 (e.g., a 3D NAND architecture semiconductormemory array) can include a number of memory cells arranged in, forexample, a number of devices, planes, blocks, or physical pages. As oneexample, a TLC memory device can include 18,592 bytes (B) of data perpage, 1536 pages per block, 548 blocks per plane, and 4 planes perdevice. As another example, an MLC memory device can include 18,592bytes (B) of data per page, 1424 pages per block, 548 blocks per plane,and 4 planes per device, but with half the required write time and twicethe program/erase (P/E) cycles as a corresponding TLC memory device.Other examples can include other numbers or arrangements.

The memory controller 111 can receive instructions from the host 105,and can communicate with the non-volatile memory 112, such as totransfer data to (e.g., write or erase) or from (e.g., read) one or moreof the memory cells of the non-volatile memory 112. The memorycontroller 111 can include, among other things, an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), orone or more other processing circuits or firmware, such as a number ofcomponents or integrated circuits. For example, the memory controller111 can include one or more memory control units, circuits, orcomponents configured to control access across the memory array and toprovide a translation layer between the host 105 and the storage system110.

In operation, in the example of NAND-based storage, data is typicallywritten to or read from the storage system 110 in “pages” and erased in“blocks.” However, one or more memory operations (e.g., read, write,erase, etc.) can be performed on larger or smaller groups of memorycells, as desired. For example, a partial update of tagged data from anoffload unit can be collected during data migration or garbagecollection to ensure it was re-written efficiently. The data transfersize of the NAND memory device is typically referred to as a page,whereas the data transfer size of a host is typically referred to as asector. Although a page of data can include a number of bytes of userdata (e.g., a data payload including a number of sectors of data) andits corresponding metadata, the size of the page often refers only tothe number of bytes used to store the user data. As an example, a pageof data having a page size of 4 KB may include 4 KB of user data (e.g.,8 sectors assuming a sector size of 512 B) as well as a number of bytes(e.g., 32 B, 54 B, 224 B, etc.) of metadata corresponding to the userdata, such as integrity data (e.g., error detecting or correcting codedata), address data (e.g., logical address data, etc.), or othermetadata associated with the user data.

Different types of memory cells or memory arrays can provide differentsize units in which data may be read, written, and erased, and incertain examples may require different amounts of metadata associatedtherewith. For example, different memory device types may have differentbit error rates, which can lead to different amounts of metadatanecessary to ensure integrity of the page of data (e.g., a memory devicewith a higher bit error rate may require more bytes of error correctioncode data than a memory device with a lower bit error rate). As anexample, an MLC NAND flash device may have a higher bit error rate thana corresponding SLC NAND flash device, and as such, may require morebytes for error data than the corresponding SLC device.

The storage system 110 can include compensation circuitry 113, such as acompensation circuit, a driver circuit, or one or more other circuitsconfigured to bias a signal line of a memory array (e.g., a memory arrayof the non-volatile memory 112) to provide functional signal lineoverdrive to reduce performance variation across the memory array, suchas settling time variance across signal lines (e.g., word lines, etc.)of the memory array. In certain examples, at least a portion of thefunctionality of the compensation circuitry 113, such as determining orcontrolling application of a compensation profile of the functionalsignal line overdrive, etc., can be implemented in one or more othercomponent of the storage system 110, such as the memory controller 111,one or more circuits or components of the non-volatile memory 112, etc.,or in one or more components of the host device 105, such as the hostprocessor 106, etc. The compensation circuitry 113 can control a drivercircuit, such as a driver of a row or column decoder, etc., to providethe functional signal line overdrive to the signal line.

FIG. 2 illustrates an example 3D NAND architecture semiconductor memoryarray 200 including N word lines 201 and first and second select gates202, 203, stacked between a source line 204 and M bit lines 205.Multiple pillars extend through the word lines 201 to create memorycells. Due to process (e.g., side and etching effects), the pillardiameter may be irregular (e.g., irregular between the multiple pillars,irregular as each pillar extends through the stacked word lines 201,etc.). Moreover, each word line can vary (e.g., in size, in surfacevariations, etc.). Accordingly, electrical parameters (e.g., resistance,capacitance, etc.) of each word line can vary with respect to the stack,affecting performance of the memory cells. Although illustrated hereinas 5 word lines and 7 bit lines, memory arrays frequently have largenumbers of each (e.g., 64, 92, 128, etc.). Electrical parameters of bitlines can also vary; however, such variance is often less than thatfound in word lines.

FIG. 3 illustrates an example distributed RC line 300 having a timeconstant characterized as a product of the resistance (R) andcapacitance (C) of the distributed RC line 300. The time constant of thedistributed RC line 300 is directly proportional to the propagationdelay of the distributed RC line 300.

Each word line of a memory array can be illustrated as a distributed RCline having respective electrical parameters that vary across the memoryarray. As the electrical parameters of the word lines vary, thepropagation delay of the word lines across the memory array varies. Toaccount for such variance in a memory array or across a storage system,a maximum propagation delay is typically assumed, limiting theperformance of the memory array or storage system.

To improve memory array performance, a signal line (e.g., a word line, abit line, etc.) can be biased at a voltage higher than the final target(K_(OD)*V_(TARGET)) of the signal line for a limited overdrive period(T_(OD)) to reduce the settling time of the signal line.

FIG. 4 illustrates example settling times of signal lines with andwithout overdrive. Signal lines are often biased to a target condition(e.g., a target voltage (V_(TARGET)) 401, a target current, etc.) beforecertain memory operations (e.g., read operations, write operations,etc.) are performed. When a target voltage (V_(TARGET)) 401 is applied,a resulting voltage builds on the signal line (V_(SL W/O OD)) 402approaching the target voltage (V_(TARGET)) 401 after a first period oftime. The target condition can include at least one of a read biasthreshold, a write bias threshold, or one or more other thresholdconditions on a signal line of a memory array or a memory device. Whenan overdrive voltage (V_(OD)) 403 above the target voltage, such as by aselected increment (e.g., an overdrive coefficient (K_(OD))), is appliedfor an overdrive period (T_(OD)) 405, a resulting voltage builds on thesignal line (V_(SL W/OD)) 404, approaching the target voltage(V_(TARGET)) 401 faster than the first period of time.

FIG. 5 illustrates an example relationship 500 between a normalizedoverdrive period (T′_(OD)) and an overdrive coefficient (K_(OD)) forstacked word lines in a memory array. The normalized overdrive period(T′_(OD)) is the overdrive period (T_(OD)) normalized by the electricalparameters of the word line (T′_(OD)=T_(OD)/RC); thus, such relationshipis valid for any process or manufacturer across a set of storage systemsor memory devices.

The present inventors have recognized a relationship between theoverdrive period (T_(OD)) and the overdrive coefficient (K_(OD)) for theminimum propagation time achievable as a function of the electricalparameters (e.g., a resistance, a capacitance, etc.) of the word linesreferred to herein as a line of minimum settling (T′_(OD)(K_(OD))) 501.Applying a specific set of T_(OD)/K_(OD) values for each word line, evenfor word lines having different electrical parameters (e.g., due toprocess, location, etc.), the same (or similar) propagation delay can beachieved across all word lines. Instead of preparing for a worst-casescenario or variance across the word lines, a configurable or minimumpropagation delay or settling time can be achieved across the wordlines, improving or providing a configurable latency or speed ofoperations on the memory array.

For example, if K_(OD)=B, then T′_(OD)=A, and T_(OD) can be set to A*RCto achieve a minimum settling time on the word line, regardless ofprocess or manufacture. Where word lines across a memory array have aresistance distribution between R_(MIN) and R_(MAX), all resistances canbe normalized by dividing by R_(MIN), and will be greater than 1 andsmaller than R_(MAX)/R_(MIN).

In an example, word lines in a memory array can be assumed to have aconstant capacitance (C). If K_(OD) is fixed to B, T_(OD)=A*RC is anoptimal T_(OD) for a word line having R=R_(MIN). For a word line havingR=R_(MAX), T_(OD)(R_(MAX))=T_(OD)(R_(MIN))*(R_(MAX)/R_(MIN)).Accordingly, T_(OD) can be scaled linearly with normalized R values. Inother examples, word lines in a memory array can have varied capacitance(C). As such, Too can be scaled linearly with normalized C values,T_(OD)*(R_(MAX)/R_(MIN))*(C_(MAX)/C_(MIN)). In other examples,resistance or capacitance distributions can be transformed into a T_(OD)distribution at a fixed K_(OD) for the same minimized settling time onthe word lines of a memory array, or into a K_(OD) distribution at afixed T_(OD) for the same minimized settling time on the word lines of amemory array.

The present inventors have further recognized, among other things, thatsettling times are not linear across the range of T_(OD) and K_(OD)values. Settling times can be reduced, for example, by as much as 60% ormore, at the line of minimum settling (T′_(OD)(K_(OD))) 501. Thederivative of the settling time is higher around the line of minimumsettling (T′_(OD)(K_(OD))) 501 than away from it. Moreover, the settlingtime is lower in a first zone 502 underneath the line of minimumsettling (T′_(OD)(K_(OD))) 501 than in zones above the line of minimumsettling (T′_(OD)(K_(OD))) 501. For example, settling time in the firstzone 502 can be reduced between 0% and 40%. However, in the zones abovethe line of minimum settling (T′_(OD)(K_(OD))) 501, settling times mayincrease in contrast to no overdrive being applied at all, by as much as40% in a second zone 503 or 60% or more in a third zone 504. Too muchoverdrive, voltage or time, can be disadvantageous. An incorrectK_(OD)/T_(OD) pair for a set of RC parameters for a given word line mayresult in an increased settling time. There may be significant benefitin applying a proper K_(OD)/T_(OD) pair to a given word line, such asusing a compensation circuit.

FIG. 6 illustrates an example compensation profile 600 (e.g., a box andwhisker plot) including trim values for a number of word lines (e.g.,word lines WL00-WL50, etc.) across a number of memory arrays. The trimvalue can selected to compensate for varying electrical parameters(e.g., R, C, a combination of R and C, etc.) across the word lines, and,in certain examples, can control one or more of a K_(OD) or a T_(OD)parameter for each word line, such as by controlling a parameter of adriver circuit (e.g., overdrive voltage, overdrive time, etc.) to reducesettling time or one or more other parameters (e.g., overdrive time orvoltage variation, etc.) across the memory array. Although illustratedherein as having 100 selectable trim values, in other examples, one ormore other numbers of trim values can be used, or a variable trim valuecan be determined and applied for each word line. The trim values can beconfigured to control a selectable or controllable output of a drivercircuit or a time of transition, such as from a first overdrive voltageto a target condition. In other examples, the trim values can beconfigured to control one or more other bias signal, such as a voltage,a current, etc.

In certain examples, a pair of K_(OD)/T_(OD) parameters can bedetermined and assigned to each word line, such as to minimize thesettling time across a memory array. In other examples, a first one ofthe K_(OD)/T_(OD) pair (e.g., T_(OD)) can be fixed across a memory arrayor a number of memory arrays in a memory system, and a second one of theK_(OD)/T_(OD) pair (e.g., K_(OD)) can be determined and assigned to eachword line. However, given the number of word lines in a memory system,the amount of information to be stored on static memory of the memorysystem, or elsewhere (e.g., on the host, etc.) can be large.Accordingly, determining and assigning separate parameters for each wordline can be storage prohibitive as well as resource/time intensive, asthe electrical parameters of each word line are measured or determinedto determine the trim for each word line. For example, if K_(OD) isfixed, and T_(OD) has an 8-bit resolution, the number of bits requiredto store the T_(OD) information can be 8 bits*#WL, where #WL is thenumber of word lines.

To reduce the amount of storage and time required to determine and applycompensation information (e.g., electrical parameters, K_(OD)/T_(OD)parameters, trim values, etc.), an algorithmic function can bedetermined using a number of compensation techniques, in combinationwith or separate from fixing one of K_(OD) or T_(OD).

FIGS. 7-9 illustrate example functional compensation profiles 700, 800,900 determined using different compensation techniques to account forvariation across word lines of a memory device. In an example, one ofK_(OD) or T_(OD) can be fixed, such as using the line of minimumsettling (T′_(OD)(K_(OD))) information from FIG. 5, so that only one ofK_(OD) or T_(OD) has to be stored. In the descriptions of FIGS. 7-9below, it is assumed that K_(OD) is fixed and T_(OD) is stored, such as.However, in other examples, T_(OD) can be fixed and K_(OD) can bestored, or both T_(OD) and K_(OD) can be stored.

FIG. 7 illustrates an example segment 701 of a functional compensationprofile 700 using a linear compensation technique to store T_(OD). In anexample, T_(OD)=A+B*(WL_(INDEX)) for 0<INDEX<N, where A and B arevariables that define the line of the linear technique 701, and N is thetotal number of word lines in the memory device. The storage requiredfor such technique can include the sum of the resolutions of variables Aand B. For example, if A and B are each 8 bits, the storage required canbe 16 bits.

FIG. 8 illustrates example first, second, third, and fourth segments801A-801D of a functional compensation profile 800 using a piece-wiselinear compensation technique to store T_(OD). In an example,T_(OD)=A+B*(WL_(INDEX)) for 0<INDEX<N*i, where A and B are variablesthat define the line of the piece-wise linear compensation technique, Nis the total number of word lines in the memory device, and i is thenumber of segments (in this example, 4). The storage required for suchtechnique can include the sum of the resolutions of variables A and Bmultiplied by the number of segments. For example, if A and B are each 8bits and there are 4 segments, the storage required can be 16*4 bits, 64bits. To save storage space, the number of segments should be less thanthe number of word lines divided by 2.

FIG. 9 illustrates example first and second segments 901A, 901B of afunctional compensation profile 900 using a piece-wise polynomialcompensation technique to store T_(OD). In an example,T_(OD)=a_(n)+a_(n-1)*(WL_(INDEX))^(n-1)+ . . . +a_(n-1)*(WL_(INDEX))^(n)for 0<INDEX<N*i, where N is the total number of word lines in the memorydevice, and i is the number of segments (in this example, 2), and n isthe degree of the polynomial (in this example, 4). The storage requiredfor such technique can include the sum of the resolution of the variablea multiplied by the number of segments and the number of variablesrequired for the degree of the polynomial (e.g., the degree of thepolynomial+1). For example, if a has a resolution of 8 bits and thereare two segments degree 4 polynomials, the storage required can be 8*5*2bits, 80 bits. The fewer the segments, the higher the degree polynomial.For example, for a degree 2 polynomial, the number of segments should beless than the number of word lines divided by 3.

In other examples, a piece-wise constant compensation technique or oneor more other techniques can be used to store T_(OD). The piece-wiseconstant compensation technique can require the sum of the resolution ofa variable representing the constant times the number of segments. Othertechniques can require other numbers of bits. In certain examples,multiple compensation techniques can be combined to cover a functionalcompensation profile, such as using different compensation techniques indifferent segments to reduce the storage required to cover thefunctional compensation profile. For example, for the first and secondsegments 901A, 901B illustrated in FIG. 9, a linear technique can beused to describe the first segment 901A and a polynomial compensationtechnique can be used to describe the second segment 901B.

In practice, determining specific values (e.g., trim values, etc.) ofthe functional compensation profile individually for each word line ofeach memory array or in each memory device may not be practical. Incertain examples, the functional compensation profile can be determinedto compensate for an average value of the distribution of electricalparameters (e.g., R, C, a combination thereof, etc.) for a given wordline for a type of memory array or memory device, and not for individualvariance across multiple memory arrays or memory devices. In an example,the compensators can be targeted at systemic process effects toword-line electrical parameters and variances, and not to the specificrandom impacts to a specific memory array or memory device.

Moreover, compensation can be more effective when RMAX/RMIN>>1 across asegment, number of segments, or all word lines of a memory array, memorydevice, or a functional compensation profile. Such compensation canrelieve the cost of memory device manufacturing and process, asexpensive process control techniques to limit wide variations of wordline electrical parameters can be avoided if they can otherwise becompensated for. In certain examples, consistent variation in electricalparameters across memory arrays or memory devices (e.g., variationspecificity), from a compensation perspective, can be more advantageousthan the magnitude of the variance in a specific device (e.g., variationsensitivity). Accordingly, use of such compensation techniques canreduce design, process, and manufacture time, as well as the time tomarket for high-performing memory devices.

FIG. 10 illustrates an example method 1000 to compensate for variance inan electrical parameter (e.g., R, C, both of R and C, etc.) across anumber of signal lines (e.g., word lines) of a memory array. In certainexamples, a relationship between an overdrive voltage (e.g., the productof a target condition (e.g., a target voltage (V_(TARGET))) and anoverdrive coefficient (K_(OD)), V_(OD)) and an overdrive period can bedetermined, such as using a compensation circuit or one or morecomponents of a memory system, a host system, or an external system orprocess. Propagation and settling times can be optimized using thedetermined relationship as a function of the electrical parameters ofthe signal line.

At 1001, a distribution of a physical parameter of a memory array isdetermined, such as using a compensation circuit, etc. In an example, aresistance distribution across the memory array can be determined, suchas R_(MAX) and R_(MIN) across signal lines of the memory array, etc. Inother examples, select values of different signal lines can bedetermined, and a distribution can be inferred using the determinedvalues. In other examples, one or more other parameters can bedetermined, such as capacitance, etc. In certain examples, an indicationof a distribution can be received, and one or more component orparameter of the distribution can be determined using the receivedindication. In other examples, the distribution can be received, such asfrom one or more other circuits or processes.

At 1002, a functional compensation profile is determined for a memoryarray, such as using a compensation circuit. In an example, thefunctional compensation profile can be determined using a relationshipbetween an overdrive period (T_(OD)) and an overdrive coefficient(K_(OD)). In other examples, determining the functional compensationprofile can include determining the relationship between the overdriveperiod and the overdrive coefficient for a specific memory array ormemory system, or for a type of memory array, system, or device. Oncethe relationship between the overdrive period and the overdrivecoefficient is determined, the functional compensation profile can bedetermined for the memory array, such as by setting a first one of theoverdrive coefficient or the overdrive period to a constant anddetermining a range of a second one of the overdrive coefficient or theoverdrive period according to an electrical parameter of the memoryarray, such as an electrical parameter of one or more signal lines(e.g., word lines) of the memory array.

In an example, the electrical parameter can include a resistance (R), acapacitance (C), or one or more other electrical parameters of thememory array, including a resistance or a capacitance of one or moresignal lines of the array of memory cells. Depending on the desiredstorage parameters and performance, an electrical parameter of one ormore signal lines can be determined across the array of memory cells. Inan example, a resistance distribution across the memory array can bedetermined, such as R_(MAX) and R_(MIN) values across the signal lines.In other examples, electrical parameters for a select number of signallines of a memory array can be determined, and the functionalcompensation profile can be determined using those determined selectvalues.

For example, for the functional compensation profile in FIG. 6, if aconstant capacitance is assumed, resistance variation of the signallines drives the shape of the functional compensation profile. If theshape is known, a select number of resistances can be measured todetermine the overall functional compensation profile, depending on thedesired compensation technique. For example, if a linear compensationtechnique is desired with a single segment, resistances of the first andleast word lines can be measured to determine the functionalcompensation profile. In other examples, electrical parameters of moreor other word lines can be measured to determine the functionalcompensation profile.

At 1003, a bias signal can be provided, such as by a bias circuit of arow decoder or a column decoder, to a signal line of the memory arrayaccording to the functional compensation profile. In an example, thebias circuit can be a component of a row decoder, and the signal linecan include a word line. In certain examples, the functionalcompensation profile can be determined by a compensation circuit andstored in memory, such as read-only memory of a memory system or one ormore other memory arrays or devices. The compensation circuit cancontrol application of the bias signal and bias signal parameters (e.g.,an overdrive coefficient, an overdrive period, etc.) to the signal line.

FIG. 11 illustrates an example schematic diagram of a 3D NANDarchitecture semiconductor memory array 1100 including a number ofstrings of memory cells (e.g., first-third A₀ memory strings1105A₀-1107A₀, first-third A_(n) memory strings 1105A_(n)-1107A_(n),first-third B₀ memory strings 1105B₀-1107B₀, first-third B_(n) memorystrings 1105B_(n)-1107B_(n), etc.), organized in blocks (e.g., block A1101A, block B 1101B, etc.) and sub-blocks (e.g., sub-block A₀ 1101A₀,sub-block A_(n) 1101A_(n), sub-block B₀ 1101B₀, sub-block B_(n)1101B_(n), etc.). The memory array 1100 represents a portion of agreater number of similar structures that would typically be found in ablock, device, or other unit of a memory device.

Each string of memory cells includes a number of tiers of charge storagetransistors (e.g., floating gate transistors, charge-trappingstructures, etc.) stacked in the Z direction, source to drain, between asource line (SRC) 1135 or a source-side select gate (SGS) (e.g.,first-third A₀ SGS 1131A₀-1133A₀, first-third A_(n) SGS1131A_(n)-1133A_(n), first-third B₀ SGS 1131B₀-1133B₀, first-third B_(n)SGS 1131B_(n)-1133B_(n), etc.) and a drain-side select gate (SGD) (e.g.,first-third A₀ SGD 1126A₀-1128A₀, first-third A_(n) SGD1126A_(n)-1128A_(n), first-third B₀ SGD 1126B₀-1128B₀, first-third B_(n)SGD 1126B_(n)-1128B_(n), etc.). Each string of memory cells in the 3Dmemory array can be arranged along the X direction as data lines (e.g.,bit lines (BL) BL0-BL6 1120-1122), and along the Y direction as physicalpages.

Within a physical page, each tier represents a row of memory cells, andeach string of memory cells represents a column. A sub-block can includeone or more physical pages. A block can include a number of sub-blocks(or physical pages) (e.g., 128, 256, 384, etc.). Although illustratedherein as having two blocks, each block having two sub-blocks, eachsub-block having a single physical page, each physical page having threestrings of memory cells, and each string having 8 tiers of memory cells,in other examples, the memory array 1100 can include more or fewerblocks, sub-blocks, physical pages, strings of memory cells, memorycells, or tiers. For example, each string of memory cells can includemore or fewer tiers (e.g., 16, 32, 64, 128, etc.), as well as one ormore additional tiers of semiconductor material above or below thecharge storage transistors (e.g., select gates, data lines, etc.), asdesired. As an example, a 48 GB TLC NAND memory device can include18,592 bytes (B) of data per page (16,384+2208 bytes), 1536 pages perblock, 548 blocks per plane, and 4 or more planes per device.

Each memory cell in the memory array 1100 includes a control gate (CG)coupled to (e.g., electrically or otherwise operatively connected to) anaccess line (e.g., word lines (WL) WL0 ₀-WL7 ₀ 1110A-1117A, WL0 ₁-WL7 ₁1110B-1117B, etc.), which collectively couples the control gates (CGs)across a specific tier, or a portion of a tier, as desired. Specifictiers in the 3D memory array, and accordingly, specific memory cells ina string, can be accessed or controlled using respective access lines.Groups of select gates can be accessed using various select lines. Forexample, first-third A₀ SGD 1126A₀-1128A₀ can be accessed using an A₀SGD line SGDA₀ 1125A₀, first-third A_(n) SGD 1126A_(n)-1128A_(n) can beaccessed using an A_(n) SGD line SGDA_(n) 1125A_(n), first-third B₀ SGD1126B₀-1128B₀ can be accessed using a B₀ SGD line SGDB₀ 1125B₀, andfirst-third B_(n) SGD 1126B_(n)-1128B_(n) can be accessed using a B_(n)SGD line SGDB_(n) 1125B_(n). First-third A₀ SGS 1131A₀-1133A₀ andfirst-third A_(n) SGS 1131A_(n)-1133A_(n) can be accessed using a gateselect line SGS₀ 1130A, and first-third B₀ SGS 1131B₀-1133B₀ andfirst-third B_(n) SGS 1131B_(n)-1133B_(n) can be accessed using a gateselect line SGS₁ 1130B.

In an example, the memory array 1100 can include a number of levels ofsemiconductor material (e.g., polysilicon, etc.) configured to couplethe control gates (CGs) of each memory cell or select gate (or a portionof the CGs or select gates) of a respective tier of the array. Specificstrings of memory cells in the array can be accessed, selected, orcontrolled using a combination of bit lines (BLs) and select gates,etc., and specific memory cells at one or more tiers in the specificstrings can be accessed, selected, or controlled using one or moreaccess lines (e.g., word lines).

In a NAND architecture semiconductor memory array, the state of aselected memory cell can be accessed by sensing a current or voltagevariation associated with a particular data line containing the selectedmemory cell. The memory array 1100 can be accessed (e.g., by a controlcircuit, one or more processors, digital logic, etc.) using one or moredriver circuits. In an example, one or more driver circuits can activatea specific memory cell, or set of memory cells, by driving a particularpotential to one or more data lines (e.g., bit lines BL0-BL2), accesslines (e.g., word lines WL0-WL7), or select gates, depending on the typeof operation desired to be performed on the specific memory cell or setof memory cells.

To program or write data to a memory cell, a programming voltage (Vpgm)(e.g., one or more programming pulses, etc.) can be applied to selectedword lines (e.g., WL4 ₀), and thus, to a control gate of each memorycell coupled to the selected word lines. Programming pulses can begin,for example, at or near 15V, and, in certain examples, can increase inmagnitude during each programming pulse application. While the programvoltage is applied to the selected word lines, a potential, such as aground potential (e.g., Vss), can be applied to the data lines (e.g.,bit lines) and substrates and thus the channels, between the sources anddrains) of the memory cells targeted for programming, resulting in acharge transfer (e.g., direct injection or Fowler-Nordheim (FN)tunneling, etc.) from the channels to the floating gates of the targetedmemory cells.

In contrast, a pass voltage (Vpass) can be applied to one or more wordlines having memory cells that are not targeted for programming, or aninhibit voltage (e.g., Vcc) can be applied to data lines (e.g., bitlines) having memory cells that are not targeted for programming, forexample, to inhibit charge from being transferred from the channels tothe floating gates of such non-targeted memory cells. The pass voltagecan be variable, depending, for example, on the proximity of the appliedpass voltages to a word line targeted for programming. The inhibitvoltage can include a supply voltage (Vcc), such as a voltage from anexternal source or supply (e.g., a battery, an AC-to-DC converter,etc.), relative to a ground potential (e.g., Vss).

As an example, if a programming voltage (e.g., 15V or more) is appliedto a specific word line, such as WL4 ₀, a pass voltage of 10V can beapplied to one or more other word lines, such as WL3 ₀, WL5 ₀, etc., toinhibit programming of non-targeted memory cells, or to retain thevalues stored on such memory cells not targeted for programming. As thedistance between an applied program voltage and the non-targeted memorycells increases, the pass voltage required to refrain from programmingthe non-targeted memory cells can decrease. For example, where aprogramming voltage of 15V is applied to WL4 ₀, a pass voltage of 10Vcan be applied to WL3 ₀ and WL5 ₀, a pass voltage of 8V can be appliedto WL2 ₀ and WL6 ₀, a pass voltage of 7V can be applied to WL1 ₀ and WL7₀, etc. In other examples, the pass voltages, or number of word lines,etc., can be higher or lower, or more or less.

Sense amplifiers can be coupled to one or more of the data lines (e.g.,first, second, or third bit lines (BL0-BL2) 1120-1122), can detect thestate of each memory cell in respective data lines by sensing a voltageor current on a particular data line.

Between applications of one or more programming pulses (e.g., Vpgm), averify operation can be performed to determine if a selected memory cellhas reached its intended programmed state. If the selected memory cellhas reached its intended programmed state, it can be inhibited fromfurther programming. If the selected memory cell has not reached itsintended programmed state, additional programming pulses can be applied.If the selected memory cell has not reached its intended programmedstate after a particular number of programming pulses (e.g., a maximumnumber), the selected memory cell, or a string, block, or pageassociated with such selected memory cell, can be marked as defective.

To erase a memory cell or a group of memory cells (e.g., erasure istypically performed in blocks or sub-blocks), an erasure voltage (Vers)(e.g., typically Vpgm) can be applied to the substrates and thus thechannels, between the sources and drains) of the memory cells targetedfor erasure (e.g., using one or more bit lines, select gates, etc.),while the word lines of the targeted memory cells are kept at apotential, such as a ground potential (e.g., Vss), resulting in a chargetransfer (e.g., direct injection or Fowler-Nordheim (FN) tunneling,etc.) from the floating gates of the targeted memory cells to thechannels.

FIG. 12 illustrates an example block diagram of a memory device 1200including a memory array 1202 having a plurality of memory cells 1204,and one or more circuits or components to provide communication with, orperform one or more memory operations on, the memory array 1202.Although shown with a single memory array 1202, in other examples, oneor more additional memory arrays, dies, or LUNs can be included herein.In certain examples, in a storage system having a number of dies orLUNs, the memory device 1200 can represent a block diagram of circuitsand components for each die or LUN. The memory device 1200 can include arow decoder 1212, a column decoder 1214, sense amplifiers 1220, a pagebuffer 1222, a selector 1224, an input/output (I/O) circuit 1226, amemory control unit 1230, and one or more driver circuits configured toprovide a bias signal to one or more signal lines (e.g., one or moreaccess lines 1206, one or more data lines 1210, etc.). In an example,the row decoder 1212 and the column decoder 1214 can include one or moredriver circuits.

The memory cells 1204 of the memory array 1202 can be arranged inblocks, such as first and second blocks 1202A, 1202B. Each block caninclude sub-blocks. For example, the first block 1202A can include firstand second sub-blocks 1202A₀, 1202A_(n), and the second block 1202B caninclude first and second sub-blocks 1202B₀, 1202B_(n). Each sub-blockcan include a number of physical pages, each page including a number ofmemory cells 1204. Although illustrated herein as having two blocks,each block having two sub-blocks, and each sub-block having a number ofmemory cells 1204, in other examples, the memory array 1202 can includemore or fewer blocks, sub-blocks, memory cells, etc. In other examples,the memory cells 1204 can be arranged in a number of rows, columns,pages, sub-blocks, blocks, etc., and accessed using, for example, accesslines 1206, first data lines 1210, or one or more select gates, sourcelines, etc.

The memory control unit 1230 can control memory operations of the memorydevice 1200 according to one or more signals or instructions received oncontrol lines 1232, including, for example, one or more dock signals orcontrol signals that indicate a desired operation (e.g., write, read,erase, etc.), or address signals (A0-AX) received on one or more addresslines 1216. One or more devices external to the memory device 1200 cancontrol the values of the control signals on the control lines 1232, orthe address signals on the address line 1216. Examples of devicesexternal to the memory device 1200 can include, but are not limited to,a host, a memory controller, a processor, or one or more circuits orcomponents not illustrated in FIG. 12.

The memory device 1200 can use access lines 1206 and first data lines1210 to transfer data to (e.g., write or erase) or from (e.g., read) oneor more of the memory cells 1204. The row decoder 1212 and the columndecoder 1214 can receive and decode the address signals (A0-AX) from theaddress line 1216, can determine which of the memory cells 1204 are tobe accessed, and can provide signals to one or more of the access lines1206 (e.g., one or more of a plurality of word lines (WL0-WLm)) or thefirst data lines 1210 (e.g., one or more of a plurality of bit lines(BL0-BLn)), such as described above.

The memory device 1200 can include sense circuitry, such as the senseamplifiers 1220, configured to determine the values of data on (e.g.,read), or to determine the values of data to be written to, the memorycells 1204 using the first data lines 1210. For example, in a selectedstring of memory cells 1204, one or more of the sense amplifiers 1220can read a logic level in the selected memory cell 1204 in response to aread current flowing in the memory array 1202 through the selectedstring to the data lines 1210.

One or more devices external to the memory device 1200 can communicatewith the memory device 1200 using the I/O lines (DQ0-DQN) 1208, addresslines 1216 (A2-AX), or control lines 1232. The input/output (I/O)circuit 1226 can transfer values of data in or out of the memory device1200, such as in or out of the page buffer 1222 or the memory array1202, using the I/O lines 1208, according to, for example, the controllines 1232 and address lines 1216. The page buffer 1222 can store datareceived from the one or more devices external to the memory device 1200before the data is programmed into relevant portions of the memory array1202, or can store data read from the memory array 1202 before the datais transmitted to the one or more devices external to the memory device1200.

The column decoder 1214 can receive and decode address signals (A0-AX)into one or more column select signals (CSEL1-CSELn). The selector 1224(e.g., a select circuit) can receive the column select signals(CSEL1-CSELn) and select data in the page buffer 1222 representingvalues of data to be read from or to be programmed into memory cells1204. Selected data can be transferred between the page buffer 1222 andthe I/O circuit 1226 using second data lines 1218.

The memory control unit 1230 can receive positive and negative supplysignals, such as a supply voltage (Vcc) 1234 and a negative supply (Vss)1236 (e.g., a ground potential), from an external source or supply(e.g., an internal or external battery, an AC-to-DC converter, etc.). Incertain examples, the memory control unit 1230 can include a regulator1228 to internally provide positive or negative supply signals.

FIG. 13 illustrates a block diagram of an example machine 1300 uponwhich any one or more of the techniques (e.g., methodologies) discussedherein may perform, such as triggering a CSAVE operation in a memorydevice (e.g., an NVDIMM) using a timer implemented using a memorycontroller of the NVDIMM. In alternative embodiments, the machine 1300may operate as a standalone device or may be connected (e.g., networked)to other machines. In a networked deployment, the machine 1300 mayoperate in the capacity of a server machine, a client machine, or bothin server-client network environments. In an example, the machine 1300may act as a peer machine in peer-to-peer (P2P) (or other distributed)network environment. The machine 1300 may be a personal computer (PC), atablet PC, a set-top box (STB), a personal digital assistant (PDA), amobile telephone, a web appliance, an IoT device, automotive system, orany machine capable of executing instructions (sequential or otherwise)that specify actions to be taken by that machine. Further, while only asingle machine is illustrated, the term “machine” shall also be taken toinclude any collection of machines that individually or jointly executea set (or multiple sets) of instructions to perform any one or more ofthe methodologies discussed herein, such as cloud computing, software asa service (SaaS), other computer duster configurations.

Examples, as described herein, may include, or may operate by, logic,components, devices, packages, or mechanisms. Circuitry is a collection(e.g., set) of circuits implemented in tangible entities that includehardware (e.g., simple circuits, gates, logic, etc.). Circuitrymembership may be flexible over time and underlying hardwarevariability. Circuitries include members that may, alone or incombination, perform specific tasks when operating. In an example,hardware of the circuitry may be immutably designed to carry out aspecific operation (e.g., hardwired). In an example, the hardware of thecircuitry may include variably connected physical components (e.g.,execution units, transistors, simple circuits, etc.) including acomputer-readable medium physically modified (e.g., magnetically,electrically, moveable placement of invariant massed particles, etc.) toencode instructions of the specific operation. In connecting thephysical components, the underlying electrical properties of a hardwareconstituent are changed, for example, from an insulator to a conductoror vice versa. The instructions enable participating hardware (e.g., theexecution units or a loading mechanism) to create members of thecircuitry in hardware via the variable connections to carry out portionsof the specific tasks when in operation. Accordingly, thecomputer-readable medium is communicatively coupled to the othercomponents of the circuitry when the device is operating. In an example,any of the physical components may be used in more than one member ofmore than one circuitry. For example, under operation, execution unitsmay be used in a first circuit of a first circuitry at one point in timeand reused by a second circuit in the first circuitry, or by a thirdcircuit in a second circuitry at a different time.

The machine (e.g., computer system) 1300 (e.g., the host 105, thestorage system 110, etc.) may include a hardware processor 1302 (e.g., acentral processing unit (CPU), a graphics processing unit (GPU), ahardware processor core, or any combination thereof, such as a memorycontroller, etc.), a main memory 1304 and a static memory 1306, some orall of which may communicate with each other via an interlink (e.g.,bus) 1330. The machine 1300 may further include a display unit, analphanumeric input device (e.g., a keyboard), and a user interface (UI)navigation device (e.g., a mouse). In an example, the display unit,input device and UI navigation device may be a touch screen display. Themachine 1300 may additionally include a signal generation device (e.g.,a speaker), a network interface device 1308, and one or more sensors,such as a global positioning system (GPS) sensor, compass,accelerometer, or other sensor. The machine 1300 may include an outputcontroller, such as a serial (e.g., universal serial bus (USB),parallel, or other wired or wireless (e.g., infrared (IR), near fieldcommunication (NFC), etc.) connection to communicate or control one ormore peripheral devices (e.g., a printer, card reader, etc.).

The machine 1300 may include a storage system (e.g., a machine-readablemedium) on which is stored one or more sets of data structures orinstructions 1326 (e.g., software) embodying or utilized by any one ormore of the techniques or functions described herein. The instructions1326 may also reside, completely or at least partially, within the mainmemory 1304, within static memory 1306, or within the hardware processor1302 during execution thereof by the machine 1300. In an example, one orany combination of the hardware processor 1302, the main memory 1304,the static memory 1306, or the storage system 1318 may constitute amachine-readable medium. The term “machine-readable medium” may includea single medium or multiple media (e.g., a centralized or distributeddatabase, or associated caches and servers) configured to store the oneor more instructions 1326.

The term “machine-readable medium” may include any medium that iscapable of storing, encoding, or carrying instructions for execution bythe machine 1300 and that cause the machine 1300 to perform any one ormore of the techniques of the present disclosure, or that is capable ofstoring, encoding, or carrying data structures used by or associatedwith such instructions. Non-limiting machine-readable medium examplesmay include solid-state memories, and optical and magnetic media. In anexample, a massed machine-readable medium comprises a machine-readablemedium with a plurality of particles having invariant (e.g., rest) mass.Accordingly, massed machine-readable media are not transitorypropagating signals. Specific examples of massed machine-readable mediamay include: non-volatile memory, such as semiconductor memory devices(e.g., Electrically Programmable Read-Only Memory (EPROM), ElectricallyErasable Programmable Read-Only Memory (EPROM)) and flash memorydevices; magnetic disks, such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

The instructions 1326 (e.g., software, programs, an operating system(OS), etc.) or other data are stored on the storage system 1318, can beaccessed by the memory 1304 for use by the processor 1302. The memory1304 (e.g., DRAM) is typically fast, but volatile, and thus a differenttype of storage than the storage system 1318 (e.g., an SSD), which issuitable for long-term storage, including while in an “off” condition.The instructions 1326 or data in use by a user or the machine 1300 aretypically loaded in the memory 1304 for use by the processor 1302. Whenthe memory 1304 is full, virtual space from the storage system 1318 canbe allocated to supplement the memory 1304; however, because the storagesystem 1318 device is typically slower than the memory 1304, and writespeeds are typically at least twice as slow as read speeds, use ofvirtual memory can greatly reduce user experience due to storage devicelatency (in contrast to the memory 1304, e.g., DRAM). Further, use ofthe storage system 1318 for virtual memory can greatly reduce the usablelifespan of the storage system 1318.

In contrast to virtual memory, virtual memory compression (e.g., theLinux™ kernel feature “ZRAM”) uses part of the memory as compressedblock storage to avoid paging to the storage system 1318. Paging takesplace in the compressed block until it is necessary to write such datato the storage system 1318. Virtual memory compression increases theusable size of memory 1304, while reducing wear on the storage system1318.

Storage systems optimized for mobile electronic devices, or mobilestorage, traditionally include MMC solid-state storage systems (e.g.,micro Secure Digital (microSD™) cards, etc.). MMC devices include anumber of parallel interfaces (e.g., an 8-bit parallel interface) with ahost, and are often removable and separate components from the host. Incontrast, eMMC™ devices are attached to a circuit board and considered acomponent of the host, with read speeds that rival serial ATA™ (SerialAT (Advanced Technology) Attachment, or SATA) based SSD devices.However, demand for mobile device performance continues to improve, suchas to fully enable virtual or augmented-reality devices, utilizeincreasing networks speeds, etc. In response to this demand, storagesystems have shifted from parallel to serial communication interfaces.Universal Flash Storage (UFS) devices, including controllers andfirmware, communicate with a host using a low-voltage signalinginterface, such as a Scalable Low-Voltage Signaling (SLVS) interfacewith dedicated read/write paths, further increasing read/write speeds.

The instructions 1326 may further be transmitted or received over acommunications network 1320 using a transmission medium via the networkinterface device 1308 utilizing any one of a number of transferprotocols (e.g., frame relay, internet protocol (IP), transmissioncontrol protocol (TCP), user datagram protocol (UDP), hypertext transferprotocol (HTTP), etc.). Example communication networks may include alocal area network (LAN), a wide area network (WAN), a packet datanetwork (e.g., the Internet), mobile telephone networks (e.g., cellularnetworks), Plain Old Telephone (POTS) networks, and wireless datanetworks (e.g., Institute of Electrical and Electronics Engineers (IEEE)802.11 family of standards known as Wi-Fi®, IEEE 802.16 family ofstandards known as WiMax®), IEEE 802.15.4 family of standards,peer-to-peer (P2P) networks, among others. In an example, the networkinterface device 1308 may include one or more physical jacks (e.g.,Ethernet, coaxial, or phone jacks) or one or more antennas to connect tothe communications network 1320. In an example, the network interfacedevice 1308 may include a plurality of antennas to wirelesslycommunicate using at least one of single-input multiple-output (SIMO),multiple-input multiple-output (MIMO), or multiple-input single-output(MISO) techniques. The term “transmission medium” shall be taken toinclude any intangible medium that is capable of storing, encoding, orcarrying instructions for execution by the machine 1300, and includesdigital or analog communications signals or other intangible medium tofacilitate communication of such software.

In Example 1, subject matter (e.g., a system) may comprise an array ofmemory cells including a number of signal lines (e.g., word lines, bitlines, etc.), each signal line configured to provide access to a numberof memory cells responsive to a bias condition of the respective signalline; and a compensation circuit configured to provide a bias signal toa first one of the number of signal lines, the bias signal having amagnitude greater than a magnitude of a target condition by an overdrivecoefficient for an overdrive period according to a functionalcompensation profile, wherein the functional compensation profilecomprises a distribution of one of the overdrive coefficient or theoverdrive period across the number of signal lines to compensate forvariance in an electrical parameter across the number of signal lines.

In Example 2, the subject matter of Example 1 may optionally beconfigured such that the functional compensation profile comprises: afirst one of the overdrive coefficient or the overdrive period fixed toa constant value; and a distribution of a second one of the overdrivecoefficient or the overdrive period across the number of signal lines tocompensate for variance in the electrical parameter across the number ofsignal lines.

In Example 3, the subject matter of any one or more of Examples 1-2 mayoptionally be configured such that the functional compensation profilecomprises: a fixed overdrive coefficient; and a distribution of theoverdrive period across the number of signal lines to compensate forvariance in the electrical parameter across the number of signal lines.

In Example 4, the subject matter of any one or more of Examples 1-3 mayoptionally be configured such that the functional compensation profilecomprises: a fixed overdrive period; and a distribution of the overdrivecoefficient across the number of signal lines to compensate for variancein the electrical parameter across the number of signal lines.

In Example 5, the subject matter of any one or more of Examples 1-4 mayoptionally be configured such that the target condition comprises a biasthreshold voltage configured to be applied to the first signal lineprior to performing a memory operation.

In Example 6, the subject matter of any one or more of Examples 1-5 mayoptionally be configured such that the functional compensation profilecomprises a number of trim values distributed across the number ofsignal lines using at least one of: a linear function; a piece-wiseconstant function; a piece-wise linear function; or a piece-wisepolynomial function.

In Example 7, the subject matter of any one or more of Examples 1-6 mayoptionally be configured such that the compensation circuit isconfigured to determine the functional compensation profile for thearray of memory cells using a relationship between the overdrivecoefficient and the overdrive period to reduce a settling time of thetarget condition on the number of signal lines.

In Example 8, the subject matter of any one or more of Examples 1-7 mayoptionally be configured to comprise a memory device, wherein the memorydevice comprises a number of arrays of non-volatile memory cellsaccording to a first manufacturer or process, wherein the functionalcompensation profile is determined for the memory device according tothe first manufacturer or process.

In Example 9, the subject matter of any one or more of Examples 1-8 mayoptionally be configured such that the compensation circuit isconfigured to determine the functional compensation profile for thearray of memory cells using a relationship between the overdrivecoefficient and the overdrive period and an electrical characteristic ofthe array of memory cells.

In Example 10, the subject matter of any one or more of Examples 1-9 mayoptionally be configured such that the electrical characteristic of thearray of memory cells comprises at least one of a resistance or acapacitance of at least one of the number of signal lines.

In Example 11, the subject matter of any one or more of Examples 1-10may optionally be configured such that the electrical characteristic ofthe array of memory cells comprises a range of resistances across thenumber of signal lines.

In Example 12, subject matter (e.g., a method) may comprise providing,using a compensation circuit, a bias signal to a first one of a numberof signal lines of an array of memory cells to access a number of memorycells responsive to a bias condition of the first signal line, the biassignal has a magnitude greater than a magnitude of a target condition byan overdrive coefficient for an overdrive period according to afunctional compensation profile, wherein the functional compensationprofile comprises a distribution of one of the overdrive coefficient orthe overdrive period across the number of signal lines to compensate forvariance in an electrical parameter across the number of signal lines.

In Example 13, the subject matter of Example 12 may optionally beconfigured such that the functional compensation profile comprises: afirst one of the overdrive coefficient or the overdrive period fixed toa constant value; and a distribution of a second one of the overdrivecoefficient or the overdrive period across the number of signal lines tocompensate for variance in the electrical parameter across the number ofsignal lines, wherein the target condition comprises a bias thresholdvoltage configured to be applied to the first signal line prior toperforming a memory operation.

In Example 14, the subject matter of any one or more of Examples 12-13may optionally be configured such that the functional compensationprofile comprises: a fixed overdrive coefficient; and a distribution ofthe overdrive period across the number of signal lines to compensate forvariance in the electrical parameter across the number of signal lines.

In Example 15, the subject matter of any one or more of Examples 12-14may optionally be configured such that the functional compensationprofile comprises: a fixed overdrive period; and a distribution of theoverdrive coefficient across the number of signal lines to compensatefor variance in the electrical parameter across the number of signallines.

In Example 16, the subject matter of any one or more of Examples 12-15may optionally be configured such that the functional compensationprofile comprises a number of trim values distributed across the numberof signal lines using at least one of: a linear function; a piece-wiseconstant function; a piece-wise linear function; or a piece-wisepolynomial function.

In Example 17, the subject matter of any one or more of Examples 12-16may optionally be configured to comprise determining the functionalcompensation profile for the array of memory cells using a relationshipbetween the overdrive coefficient and the overdrive period to reduce asettling time of the target condition on the number of signal lines.

In Example 18, the subject matter of any one or more of Examples 12-17may optionally be configured to comprise determining the functionalcompensation profile for the array of memory cells using a relationshipbetween the overdrive coefficient and the overdrive period and anelectrical characteristic of the array of memory cells.

In Example 19, the subject matter of any one or more of Examples 12-18may optionally be configured such that the electrical characteristic ofthe array of memory cells comprises at least one of a resistance or acapacitance of at least one of the number of signal lines.

In Example 20, the subject matter of any one or more of Examples 12-19may optionally be configured such that the electrical characteristic ofthe array of memory cells comprises a range of resistances across thenumber of signal lines.

In Example 21, subject matter (e.g., a system or apparatus) mayoptionally combine any portion or combination of any portion of any oneor more of Examples 1-20 to comprise “means for” performing any portionof any one or more of the functions or methods of Examples 1-20, or a“non-transitory machine-readable medium” including instructions that,when performed by a machine, cause the machine to perform any portion ofany one or more of the functions or methods of Examples 1-20.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples”. Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” may include “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein”. Also, in the following claims, theterms “including” and “comprising” are open-ended. A system, device,article, or process that includes elements in addition to those listedafter such a term in a claim are still deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects.

In various examples, the components, controllers, processors, units,engines, or tables described herein can include, among other things,physical circuitry or firmware stored on a physical device. As usedherein, “processor” means any type of computational circuit such as, butnot limited to, a microprocessor, a microcontroller, a graphicsprocessor, a digital signal processor (DSP), or any other type ofprocessor or processing circuit, including a group of processors ormulti-core devices.

Operating a memory cell, as used herein, includes reading from, writingto, or erasing the memory cell. The operation of placing a memory cellin an intended state is referred to herein as “programming,” and caninclude both writing to or erasing from the memory cell (e.g., thememory cell may be programmed to an erased state).

According to one or more embodiments of the present disclosure, a memorycontroller (e.g., a processor, controller, firmware, etc.) locatedinternal or external to a memory device, is capable of determining(e.g., selecting, setting, adjusting, computing, changing, clearing,communicating, adapting, deriving, defining, utilizing, modifying,applying, etc.) a quantity of wear cycles, or a wear state (e.g.,recording wear cycles, counting operations of the memory device as theyoccur, tracking the operations of the memory device it initiates,evaluating the memory device characteristics corresponding to a wearstate, etc.)

According to one or more embodiments of the present disclosure, a memoryaccess device may be configured to provide wear cycle information to thememory device with each memory operation. The memory device controlcircuitry (e.g., control logic) may be programmed to compensate formemory device performance changes corresponding to the wear cycleinformation. The memory device may receive the wear cycle informationand determine one or more operating parameters (e.g., a value,characteristic) in response to the wear cycle information.

It will be understood that when an element is referred to as being “on,”“connected to,” or “coupled with” another element, it can be directlyon, connected, or coupled with the other element or intervening elementsmay be present. In contrast, when an element is referred to as being“directly on,” “directly connected to,” or “directly coupled with”another element, there are no intervening elements or layers present. Iftwo elements are shown in the drawings with a line connecting them, thetwo elements can be either be coupled, or directly coupled, unlessotherwise indicated.

Method examples described herein can be machine, device, orcomputer-implemented at least in part. Some examples can include acomputer-readable medium, a device-readable medium, or amachine-readable medium encoded with instructions operable to configurean electronic device to perform methods as described in the aboveexamples. An implementation of such methods can include code, such asmicrocode, assembly language code, a higher-level language code, or thelike. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, the code can be tangibly stored on one ormore volatile or non-volatile tangible computer-readable media, such asduring execution or at other times. Examples of these tangiblecomputer-readable media can include, but are not limited to, hard disks,removable magnetic disks, removable optical disks (e.g., compact discsand digital video disks), magnetic cassettes, memory cards or sticks,random access memories (RAMS), read only memories (ROMs), solid statedrives (SSDs), Universal Flash Storage (UFS) device, embedded MMC (eMMC)device, and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment, and it is contemplated that such embodiments can be combinedwith each other in various combinations or permutations. The scope ofthe invention should be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

The invention claimed is:
 1. A system comprising: an array of memorycells including multiple signal lines, each signal line configured toprovide access to a group of memory cells responsive to a bias conditionof the respective signal line; and a compensation circuit configured toprovide a respective bias signal to each of the multiple signal lines,each respective bias signal having an overdrive voltage greater than atarget voltage by a selected one of a stored distribution of incrementsacross the multiple signal lines and a selected overdrive period tocompensate for variance in an electrical parameter across the signallines, wherein the selected overdrive period s fixed to a constantvalue.
 2. The system of claim 1, wherein the target voltage comprises abias threshold voltage configured to be applied to a first signal lineprior to performing a memory operation.
 3. The system of claim 1,wherein the compensation circuit comprises multiple trim values toprovide the respective bias signal, the multiple trim values distributedacross the multiple signal lines using at, least, one of: a linearfunction; a piece-wise constant function; a piece-wise linear function;or a piece-wise polynomial function.
 4. The system of claim 1,comprising a memory device, wherein the memory device comprises multiplearrays of non-volatile memory cells, wherein the compensation circuit isconfigured to determine the bias signals for the multiple signal linesusing a relationship between the selected increments and the selectedoverdrive period to reduce a settling time of the target voltage on themultiple signal lines.
 5. The system of claim 1, wherein thecompensation circuit is configured to determine the bias signals for themultiple signal lines using a relationship between the selectedincrement, and the selected overdrive period and an electricalcharacteristic of the array of memory cells.
 6. The system of claim 5,wherein the electrical characteristic of the array of memory cellscomprises at least one of a resistance or a capacitance of at least oneof the multiple signal lines.
 7. The system of claim 5, wherein theelectrical characteristic of the array of memory cells comprises a rangeof resistances across the multiple signal lines.
 8. A system comprising:an array of memory cells including multiple signal lines, each signalline configured to provide access to a group of memory cells responsiveto a bias condition of the respective signal line; and a compensationcircuit configured to provide a respective bias signal to each of themultiple signal lines, each respective bias signal having an overdrivevoltage greater than a target voltage by a selected increment and aselected one of a stored distribution of overdrive periods across themultiple signal lines to compensate for variance in an electricalparameter across the signal lines, wherein the selected increment isfixed to a constant value.
 9. The system of claim 8, wherein the targetvoltage comprises a bias threshold voltage configured to be applied to afirst signal line prior to performing a memory operation.
 10. The systemof claim 8, wherein the compensation circuit comprises multiple trimvalues to provide the respective bias signal, the multiple trim valuesdistributed across the multiple signal lines using at least one of: alinear function; a piece-wise constant function; a piece-wise linearfunction; or a piece-wise polynomial function.
 11. The system of claim8, comprising a memory device, wherein the memory device comprisesmultiple arrays of non-volatile memory cells, wherein the compensationcircuit is configured to determine the bias signals for the multiplesignal lines using a relationship between the selected increments andthe selected overdrive period to reduce a settling time of the targetvoltage on the multiple signal lines.
 12. The system of claim 8, whereinthe compensation circuit is configured to determine the bias signals forthe multiple signal lines using a relationship between the selectedincrement and the selected overdrive period and an electricalcharacteristic of the array of memory cells.
 13. The system of claim 12,wherein the electrical characteristic of the array of memory cellscomprises at least one of a resistance or a capacitance of at least oneof the multiple signal lines.
 14. The system of claim 12, wherein theelectrical characteristic of the array of memory cells comprises a rangeof resistances across the multiple signal lines.
 15. A methodcomprising: providing, using a compensation circuit, a respective biassignal to each of multiple signal lines of an array of memory cells toaccess a group of memory cells responsive to a bias condition of therespective signal line, each respective bias signal having an overdrivevoltage greater than a target voltage by a selected one of a storeddistribution of increments across the multiple signal lines and aselected overdrive period to compensate for variance in an electricalparameter across the signal lines, wherein the target voltage comprisesa bias threshold voltage configured to be applied to a first signal lineprior to performing a memory operation.
 16. The method of claim 15,wherein the selected overdrive period is fixed to a constant value. 17.The method of claim 15, comprising determining, using the compensationcircuit, the bias signals for the multiple signal lines using arelationship between the selected increments and the selected overdriveperiod and an electrical characteristic of the array of memory cells,wherein providing the respective bias signals comprise using multipletrim values distributed across the multiple signal lines using at leastone of: a linear function; a piece-wise constant function; a piece-wiselinear function; or a piece-wise polynomial function.
 18. A methodcomprising: providing, using a compensation circuit, a respective biassignal to each of multiple signal lines of an array of memory cells toaccess a group of memory cells responsive to a bias condition of therespective signal line, each respective bias signal having an overdrivevoltage greater than a target voltage by a selected increment and aselected one of a stored distribution of overdrive periods across themultiple signal lines to compensate for variance in an electricalparameter across the signal lines, wherein the target voltage comprisesa bias threshold voltage configured to be applied to a first signal lineprior to performing a memory operation.
 19. The method of claim 18,wherein the selected increment is fixed to a constant value.
 20. Themethod of claim 18, comprising determining, using the compensationcircuit, the bias signals for the multiple signal lines using arelationship between the selected increments and the selected overdriveperiod and an electrical characteristic of the array of memory cells,wherein providing the respective bias signals comprise using multipletrim values distributed across the multiple signal lines using at leastone of: a linear function; a piece-wise constant function; a piece-wiselinear function; or a piece-wise polynomial function.